Sunlight Sterilization of Water

[Turtle]

Originally Posted by freeztar

I'm unable to find studies related to UV effectiveness, can you please provide some sources?

i found some stuff.

Ultraviolet - Wikipedia, the free encyclopedia

The Sun emits ultraviolet radiation in the UVA, UVB, and UVC bands, but because of absorption in the atmosphere's ozone layer, 98.7% of the ultraviolet radiation that reaches the Earth's surface is UVA. (Some of the UVB and UVC radiation is responsible for the generation of the ozone layer.)

Ordinary glass is partially transparent to UVA but is opaque to shorter wavelengths while Silica or quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm.[4][5][6] ...

Ultraviolet Water Sterilization | BuyUV.com

Ultraviolet radiation is a type of light, unlike visible light, that cannot be seen. Its wavelengths, expressed in Angstrom units (one Angstrom unit wavelength equals one hundred-millionth of a centimeter), are shorter than the wavelengths of visible light and carry more energy. Because of this high concentration of energy, UV radiation has the unique ability to kill microorganisms with which it comes in contact.

HOW DOES ULTRAVIOLET RADIATION WORK?

Ultraviolet radiation sterilizes water. Sterilization implies that life such as bacteria, viruses, yeasts, molds, and algae are destroyed. For UV radiation to work, a 2537 Angstrom unit (254 nanometers) wavelength must come in contact with the microorganism to inactivate it. When ultraviolet rays reach the microorganism, they strike the heart of the organism destroying the DNA (deoxyribonucleic acid) and preventing it from reproducing. Table I give the amount of UV necessary to kill various microorganisms.

a list of some 'germs' and the UV dose needed to kill them: >> Germicidal Disinfection Information

Originally Posted by lemit

This is fascinating.

I've had giardia. I went for two months before I got it diagnosed. It isn't fun and I wouldn't recommend it, but I've had worse.

Where I grew up, we had water from a deep well about a half mile from a coal vein. It stuck to your ribs and probably provided more than the daily requirements of a lot of mineral supplements.

Speaking of where I grew up, if you aren't trying to make a hip-pocket purifier, how about a still like some folks back there had? Wouldn't that do the job?

That isn't a leading question. I don't know much about purifying. I wish I had when I was drinking that oily stuff.

--lemit

a still is ideal. for my hip-pocket needs, well, rucksack, i'm currently using a fiber/charcoal filter unit, and i carry a little bottle of bleach too. as it is, it would be a rare thing for me these days to take an adventure without taking all the water i need.

[InfiniteNow]

Originally Posted by Mercedes Benzene

Could you paint it black?

In addition to just painting it black, you can get much higher temps with the same amount of sunlight by increasing the pressure inside the glass. Granted, this may very well be beyond what Turtle was thinking, or might require higher tech resources than he'd planned to use, but by pressurizing the tube itself you can get a LOT more bang for each solar buck.

I'm thinking of something similar to the evacuated tubes they use in many new solar hot water heater applications.

Beyond Oil Solar: Solar Evacuated Tubes

[Turtle]

Originally Posted by InfiniteNow

In addition to just painting it black, you can get much higher temps with the same amount of sunlight by increasing the pressure inside the glass. Granted, this may very well be beyond what Turtle was thinking, or might require higher tech resources than he'd planned to use, but by pressurizing the tube itself you can get a LOT more bang for each solar buck.

I'm thinking of something similar to the evacuated tubes they use in many new solar hot water heater applications.

Beyond Oil Solar: Solar Evacuated Tubes

kewl units!
what i was really going for with my original idea was the UV doing the work, but I suspect that a magnifying glass won't bend UV to the focus, and second, the lens may absorb 90% or more of the UV that does strike it. oh well.

[modest]

Originally Posted by Turtle

i found some stuff.

a list of some 'germs' and the UV dose needed to kill them: >> Germicidal Disinfection Information

I think that info should give an idea if whether your UltraViolet Portable Absorption Sterilizing System (UV-PASS ) should work.

According to the chart you link, bacteria need between 3620 and 22000 microwatts per centimeter squared of UV to be sterilized. The only convincing source I could find on the amount of UV the earth's surface receives is this page. It gives between approx. 400 and 1800 µW/cm² for UV-A.

Needing 22,000 µW/cm² and having (on the low end) 500 µW/cm², you would need the surface of the magnifying glass to be (22000 / 500) 44 times larger than the surface of the target. That's not that bad really. If the target is one square centimeter then that's only a magnifying glass with a radius of (sqrt(44/pi)) 3.74 centimeters which is a diameter of about 3 inches.

That sounds very doable. The only thing I would worry about is how much UV the magnifying glass and the glass tube absorb. If it is something like 50 percent each then you'd have to make the area of the magnifying glass 4 times larger.

In thinking about whether the above numbers could be correct I'm reminded that my UV light keeping my pond clear of algae is 9 watts and I figure the surface area it illuminates is about 315 cm² which comes out to 38,100 µW/cm² which isn't much higher than the 22,000 that the magnifying glass with a diameter of 3 inches would achieve. And my UV light is very good at killing algae and water moves through the light very quickly.

I would wonder about parasites though. According to your chart protozoa require quite a bit more UV to kill. Are water-borne parasites protozoa? I wonder if that's the kind of thing the chart is referring to between 26,400 and 318,000 µW/cm². It would be discouraging if the intensity needed to be that high, but this is encouraging:

The United States Department of Health has determined that a UV system should provide a minimum of 16,000 Microwatts per Centimeter Square.

Information on portable water purification and portable water systems

~modest

[Turtle]

Originally Posted by modest

I think that info should give an idea if whether your UltraViolet Portable Absorption Sterilizing System (UV-PASS ) should work.

According to the chart you link, bacteria need between 3620 and 22000 microwatts per centimeter squared of UV to be sterilized. The only convincing source I could find on the amount of UV the earth's surface receives is this page. It gives between approx. 400 and 1800 µW/cm² for UV-A.

Needing 22,000 µW/cm² and having (on the low end) 500 µW/cm², you would need the surface of the magnifying glass to be (22000 / 500) 44 times larger than the surface of the target. That's not that bad really. If the target is one square centimeter then that's only a magnifying glass with a radius of (sqrt(44/pi)) 3.74 centimeters which is a diameter of about 3 inches.

That sounds very doable. The only thing I would worry about is how much UV the magnifying glass and the glass tube absorb. If it is something like 50 percent each then you'd have to make the area of the magnifying glass 4 times larger.

roger all that, and nice acronym. your source below says

pure-fused Quartz which has a transmission rate of approximately 98 percent.

my hand lens is plastic and i couldn't find much on its transmissibility of UV, but i found a lot on how damaging UV is to plastic. so, if we have ourselves a pure-fused quartz lens & tube, i still have questions/doubts whether the lens will bend the UV to the focus or if it will simply pass straight through??

Originally Posted by M-Man

I would wonder about parasites though. According to your chart protozoa require quite a bit more UV to kill. Are water-borne parasites protozoa? I wonder if that's the kind of thing the chart is referring to between 26,400 and 318,000 µW/cm². It would be discouraging if the intensity needed to be that high, but this is encouraging:

not sure on the protazoa/parasite business. will have a look.

Originally Posted by Modestino

The United States Department of Health has determined that a UV system should provide a minimum of 16,000 Microwatts per Centimeter Square.

Information on portable water purification and portable water systems

~modest

since they don't mention parasites/protazoa there as far as their UV sterilization systems, and they do have a pretreating filter in front of the UV treatment in those systems, maybe they filter out the parasites/protazoa? more sleuthing.

[Moontanman]

Dudes, and possibly dudettes, you seem to think that all UV is created equally. There is UV and then there is UV UVC and even shorter wave lengths is what is used to sterilize water. UVA and UVB rain down on the earth all the time, a great many microbes have adapted to them and are very resistant to them. The UV in sun light is not particularly germicidal. it can be on some organisms but to rely on it to sterilize water I am going to drink..... well you drink it not me..... Even if you are using germicidal UV light from a dedicated UV sterilizer it can be very tricky to get 100% sterilization even in several passes. i helped designed a UV sterilizer for the DuPont company when i worked there, It was a very difficult to achieve 100% , even tiny globs of organic material can protect microbes from the UV. If you must use sunlight use it to boil the water do not rely on UV in sunlight to sterilize anything.

[Turtle]

Originally Posted by Moontanman

Dudes, and possibly dudettes, you seem to think that all UV is created equally. There is UV and then there is UV UVC and even shorter wave lengths is what is used to sterilize water. UVA and UVB rain down on the earth all the time, a great many microbes have adapted to them and are very resistant to them. The UV in sun light is not particularly germicidal. it can be on some organisms but to rely on it to sterilize water I am going to drink..... well you drink it not me..... Even if you are using germicidal UV light from a dedicated UV sterilizer it can be very tricky to get 100% sterilization even in several passes. i helped designed a UV sterilizer for the DuPont company when i worked there, It was a very difficult to achieve 100% , even tiny globs of organic material can protect microbes from the UV. If you must use sunlight use it to boil the water do not rely on UV in sunlight to sterilize anything.

please read the links we have provided regarding UV & Sunlight; they cover your objections & misunderstandings.

[Moontanman]

I have read them turtle, when they say UV sterilization they are not talking about the UV in sunlight, they are talking about the UV from a germicidal lamp. Huge difference! I have built several UV sterilizers for my own use and for commercial use, even with germicidal lamps it is difficult to do, the water must be filtered so no particles bigger than the organisms is in the water. It still takes time to kill bacteria, protozoans are harder to kill and require much more time. A germicidal lamp can blind you fairly quickly, it can kill you, burn you severely, UV we get on the surface of the earth is not any were close to being as strongly germicidal. I see no way to use the UV in sunlight to sterilize water from a non-potable source.

[Turtle]

Originally Posted by Moontanman

I have read them turtle, when they say UV sterilization they are not talking about the UV in sunlight, ....

erhm...uh...post #4

Step 4 Utilize the effect of ultraviolet radiation on the most common pathogens. This is of particular use if you are in a circumstance where large amounts of sterile water are needed and you have few resources. Pour off particle matter. Take the clear water and pour it into a clear plastic bottle. Place the plastic bottle on a dark surface. Leave the bottle in sunlight for at least eight hours. The combined effect of ultraviolet radiation from sunlight and heat is effective in producing a primarily safe source of drinking water.

[modest]

Originally Posted by Moontanman

A germicidal lamp can blind you fairly quickly, it can kill you, burn you severely, UV we get on the surface of the earth is not any were close to being as strongly germicidal.

Well, focusing sunlight through a 3 inch lens could blind you quicker than a UV lamp (or burn you quicker). But, I think you have a sound point. There's a big difference between the UV-A which reaches Earth's surface and the optimum (middle) 254 nm for killing little buggers. The other day when I was writing the post above I found a source saying about 5 µW/cm² of UV-B reachs the surface. I've lost the link now, but if true, that is not enough in-and-of-itself to do any real damage with a moderately-sized lens.

The real question then, is how well UV-A works as a germicide. I don't know. If it's even half as effective as the middle range of UV frequencies then I believe Turtle's idea could work very well.

~modest